For many donor-conceived children, not knowing who their biological father is has led to many mixed emotions.

Kathleen learned she was a donor-conceived child when she was 8 years old. "My mom sat on my bed upstairs, and she just said that, 'Your dad is still your dad on your birth certificate, but I had to go to a sperm bank to conceive you,'" Kathleen says.

Now 26, Kathleen says having no information about the donor's medical history, heritage or family has been frustrating. She isn't even sure if her donor father knows she exists. "To me, it feels like the death of my biological father and half of my family. I've been searching, and I can't find them."

Kathleen's search has centered on the few facts she knows about her donor dad—he was enrolled in medical school at Baylor College in 1981. Over the years, she's written 600 letters to men who fit that description and received 220 responses. Despite 15 DNA tests in one year, she still doesn't have any answers.

Over the years, Kathleen says her feelings about not knowing her biological father have changed. "When I was younger, it was more of the curiosity, like why am I who I am and what did I get from my biological father? How am I like him? How am I different from him?'" Kathleen says. "Then as I got older, it became more grief and more anger, and I just feel like it should be my right to know who this man is."

Finding the donor, Kathleen says, would make a big difference in her life. "I feel like it would put the pieces of my life together and it would provide information about who I am that many people just take for granted."